I own a 2003.5 and I like mine very much too. Nothing is changed too much mechanically. Performance wise, both cars are the same basically. The clutch in 03.5 did get a more "heavy-duty" clutch, that's the word from my salesman, so judge it in your own exp. Most of the differences are comestic. Side skirts, choice of colors, spoilers, rims, interior seats, shift knobs, pedals, front lips, rear skirts, and no fog. If you don't care for the looks or color, go for a 2003 car, they could be easier to deal with. Right now the 2003.5 are just coming in, so it might be a little to get a deal down then a 2003 sitting on the lot for a couple of months. I got 2003.5, cuz I like the looks, cuz I hate fog lights on non-rally car that's all. And all the sparco stuff doesn't flow well with the mazdaspeed then then all mazdaspeed in in the inside like 2003.5.
Not dissing 03 here, just I love my 03.5 more